In the chemical process industry process streams are frequently mixed prior to reacting or shipment off site. The mixing process normally consists of simply combining the streams in a pipeline junction or tank. If the streams are of substantially different temperature, this simple process is highly irreversible thermodynamically, and considerable entropy production (lost work) occurs. In practical terms this means that an opportunity to pump heat to a higher temperature or to convert heat into work has been forever lost.
Some prior art is available concerning stream mixing prior to reaction. In U.S. Pat. No. 4,345,915, a process is described for improving water vaporization into a reactant gas stream. Thus is described as to the preparation of the gaseous reactant feed to undergo a chemical reaction requiring the presence of steam, the efficiency of overall power utilization is improved by premixing the gaseous reactant feed with water and then heating to evaporate the water in the presence of the gaseous reactant feed, the heating fluid utilized being at a temperature below the boiling point of water at the pressure in the volume where the evaporation occurs.
A direct heat transfer from a low grade heat medium is described in U.S. Pat. No. 4,072,625. In a process of reacting a hydrocarbon with steam and/or carbon dioxide in a reaction zone heated by a combustion furnace to give olefins or process gas containing carbon oxides and hydrogen high grade heat is recovered from furnace flue gases and/or process gas whereby to cool such gases to 150-300.degree. C. When the process gas is used in a synthesis of for example methanol or ammonia, gases at 150.degree.-300.degree. C are also produced. Previously the recovery of heat from such low grade heat sources has been inefficient or inconvenient. According to the invention the heat is recovered by means of an intermediary liquid coolant, which is brought into direct heat exchange with streams to be used in the process. Preferably the liquid is water under pressure and is brought into direct heat exchange with a gas to be fed to the process; by this means 10-30% of the steam can be provided from low grade waste heat.
The skilled persons in the art of mixing streams appear to focus on achieving uniform mixing instead of reducing lost work. An example of such focus in U.S. Pat. No. 5,658,503, wherein a device is provided for mixing two fluids, one a liquid, the other a gas, where apertures are provided in channel tubes to mix the fluids in the individual channels. The mixing device provides a two fluid admixture for passage to downstream processing, most preferably the tubeside of a shell and tube heat exchanger. The apparatus provides uniform distribution of gas and liquid to all parallel channels. Another such example is found in U.S. Pat. No. 5,492,409 "Device for mixing two fluids having different temperature", which describes a device for mixing two fluids having different temperatures having a connecting branch extending into a main pipe from a secondary pipe, said connecting branch having at its end positioned in the main pipe a distribution casing with double annular walls, of which an inner wall defines a channel extending axially and centrally in the main pipe, and having apertures which allow a fluid to be conducted into and mixed with the fluid passing through the main pipe. The apertures consist of a plurality of small apertures which are formed in the inner wall of the distribution casing and provide intermixing of the two fluids directly in the channel positioned centrally in the main pipe.
Tangentially, thermodynamic efficiency has been discussed with reference to distillation in U.S. Pat. No. 4,551,979 "Method and apparatus for a thermodynamic cycle by use of distillation". In that patent, a working fluid in the gaseous state at some initial temperature and pressure is expanded polytropically to a resulting exhaust fluid having some lower temperature and pressure in order to produce useful work. Large quantities of a motive liquid are then employed as the vehicle for approximating an isenthalpic compression of the working fluid. The preferred method for effecting this recompression is to reduce both fluids to a single liquid phase which is then energized. Thereafter the two fluids can be reconstituted to their initial states to complete the thermodynamic cycle which, depending upon the fluids selected, can be located in a broad range of the temperature spectrum.